The invention relates to a device in a deck for playing information discs, which preferably have been provided or can be provided with digital information, the information disc being rotated, in the operating condition, about its center by means of a drive motor and magnetically cooperating material parts being present, which are offset radially with respect to the axis of rotation and in the direction thereof parallel with respect to one another and of which one part is disposed on the base plate which carries the motor and of which the other part is disposed on the disc support which is moved by the motor shaft, one of the material parts being a ring-shaped permanent magnet.
WO 91/10996 discloses a deck for CD discs, which has magnet arrangements that serve to preclude play of the motor shaft. For this purpose, one embodiment has a permanent magnet ring and a ferromagnetic circular segment mounted on a base plate. The shaft of a drive motor extends through the permanent magnet ring without contact. The disc support carries a ferromagnetic disc. The permanent magnet and the disc are arranged centrically in parallel radial planes with respect to the axis of rotation of the system, offset from one another in the direction of the axis of rotation.
In another embodiment the permanent magnet ring is mounted on the disc support. The ferromagnetic circular segment is bent out of the base plate and is arranged closely adjacent the permanent magnet ring.
The magnetic force of attraction between the permanent magnet and the ferromagnetic disc ensure that axial play is eliminated. The ferromagnetic circular segment serves to preclude radial play of the motor shaft with the aid of the magnetic force of attraction.
This construction has the disadvantage that the circular segment continually produces impulse-like fluctuations of the magnetic field and has an adverse effect on the motor power.
Moreover, it is known from U.S. Pat. No. 4,730,299 to construct the ferromagnetic part on the disc support as a disc in order to preclude axial play.
It is an object of the invention to provide a device in a deck for playing information discs, which precludes axial and radial play of the motor shaft by means of a simple and flat construction which does not give rise to load fluctuations of the motor and is without wear.
According to the invention said object is achieved in that at least one of the two magnetically cooperating material parts is arranged eccentrically with respect to the axis of rotation and both material parts are ring-shaped, the directions of the lines of field not being changed during rotation.
This eccentric construction has the advantage that only two magnetically cooperating ring-shaped material parts are required in order to eliminate both axial and radial play of the motor shaft. Depending on the requirements both or only one of the two magnetically cooperating material parts may be permanent magnetic. As a result of the continuously ring-shaped construction of the two cooperating material parts the directions of the lines of field does not change during rotation.
In a further embodiment of the invention the two magnetically cooperating material parts surround the axis of rotation at a distance and the inner diameter and the outer diameter are substantially equal. The combined exerted forces lead to a play compensation which is uniform and, in particular, impulse free.
In a further embodiment of the invention the ring-shaped material part which forms a ferromagnetic ring is a part of the ferromagnetic motor support, which part is a raised portion around the motor shaft and forms a ring in a higher plane, which ring surrounds the motor shaft at a distance. The ferromagnetic ring thus forms a part of the motor support.
An embodiment of the invention is constructed in such a manner that the material part formed as a permanent magnet ring is arranged centrically on the disc support in a radial plane parallel to the ferromagnetic ring which is disposed eccentrically with respect to the motor shaft. In this case the ferromagnetic ring and the permanent magnet ring are superposed eccentrically with respect to one another.
In this embodiment it has proved to be effective when the permanent magnet ring is axially magnetized.
Another embodiment of the invention is constructed in such a manner that the permanent magnet ring is arranged centrically on the disc support in one radial plane with the ferromagnetic ring which is disposed eccentrically with respect to the motor shaft. This means that in this way the overall height can be reduced.
In this embodiment it has proved to be effective if the permanent magnet ring is radially magnetized.